38Q CHANGES SUCCEEDING IMPREGNATION. CHAP. VIII. 



now easily separated from the chorion ; the third 

 being the pyrena; and the fourth being the pulpy 

 pericarp. 



On the 20th, the four concentric circles of the 

 transverse section were still distinctly visible, but less 

 easily separated. 



On the 22d, the longitudinal section exhibited 

 similar appearances, but no traces of the amnios or 

 embryo were yet perceptible. 



On the 24 th, the parts were considerably enlarged, 

 but still soft and pulpy. The two middle circles 

 were the firmest ; but it was now more difficult to 

 detach the envelope of the nucleus from the in- 

 terior mass. 



On the 1 st of June, the exterior pulp was con- 

 siderably augmented in size, and the pyrena, in 

 some individuals, pretty hard. JThe sap vessels of 

 the foot-stalk were seen to enter the pyrena at the 

 lower extremity, and afterwards to emerge from its 

 interior surface rather above the middle, forming 

 the external umbilical cord and testa, or secundina 

 exterior of Malpighi, from the inner surface of 

 which they were again seen to emerge at the lower 

 extremity and to form the internal umbilical cord ; 

 which, entering the chorion at the base and passing 

 on in the direction of its longitudinal axis, termi- 

 nated ultimately in the sacculus colliquamenti and 

 amnios, now visible for the first time in the apex of 

 the chorion ; the sacculus being apparently a pro- 



2 



